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13.7: Cosmos And Culture

The End Of The Universe, The Higgs And All The 'Ifs'

Don't panic! The end of the Universe (as we know it) isn't likely to hit us for billions of years, if it comes at all. Pictured: the Milky Way rises above the ESO's ALMA facility in Chile.

José Francisco SalgadoESO

As if calling the Higgs particle "the God particle" didn't cause enough confusion and misinformation, here we go again, with the Higgs hitting the spotlight once more, but now as prophet of doom.

Yes, dear readers, it seems that the destiny of the Universe is in the hands of this particle or, more precisely, of the value of its mass.

Everything starts in the kitchen, an excellent laboratory for the physical sciences (and others). As we know, the properties of a substance, say, water, depend on its temperature: too cold, and water freezes; too hot, and it becomes steam. These changes in water and many other substances (simple and complex) are known as phase transitions.

Quite surprisingly, the Universe itself — or the matter within it — went through at least one or two phase transitions, if not more. And it could happen again.

Our cosmic history begins at the Big Bang, the event that marks the beginning of time. Right after the bang, space started to expand like a balloon and the matter and radiation within it got progressively cooler. Back to the kitchen, we see that the expansion of the Universe works as a kind of refrigerator, causing the temperature to go down. Did matter in the early stages of cosmic history also pass through a phase transition?

We know that it did. Very early on, the temperature was so high that particles had no mass. (Think, minimally, of electrons and quarks. There were others, but it doesn't make a difference to our argument.) The one particle that did have a mass was the Higgs; but it didn't interact yet with the other particles.

As the temperature dropped, the Higgs started to interact with the other particles with more intensity, giving them what it can, their masses. This process of getting a mass — related to the growing intensity of the interaction of the Higgs with the other particles — is a phase transition that happened when the cosmos was about a trillionth of a second old. (This may seem like a ridiculously small time; but for particles, it's an eternity.)

The problem is that the mass of the presumed Higgs boson is somewhere between 124 and 126 times that of a proton. With such a mass value for the Higgs, the Universe could go through another phase transition. It's as if we were in a liquid phase and could decay into a solid phase in the future. When a phase transition of this kind happens, bubbles of the new phase suddenly appear within the old phase (where we are) and expand very quickly. In cosmology, with a speed near that of light. These bubbles collide with one another, finally converting the whole volume to the new phase.

It would be the end of the Universe, at least as we know it today.

Before causing widespread panic or being accused of needless alarmism, I do have some good news. The calculations indicating that the Higgs mass is dangerously close to the value that would indicate phase instability are based in the supposition that no new physics exists between the energies probed by CERN and those near the beginning of time, a difference of 16 orders of magnitude (ten-thousand trillion). Although this is possible, it is highly improbable. New physics could rescue our phase, making it the stable one.

The calculations are also very sensitive to the exact values of certain particles (for the experts, the top quark and the strong coupling constant), which are presently known only within a fairly large window. Furthermore, and best of all, even if unstable, the calculations also show that our current phase is very long-lived: we are safe for billions of years.

(But, being a bit perverse, it is always possible that new physics could also help destabilize our phase faster; we will only know when we can probe higher energy interactions.)

As a last pacifier, even if a bubble were to pop up somewhere in the Universe, odds are it will be very far from us. So, even if traveling at the speed of light, it will take billions of years to get to us.

To summarize, the possibility that we live in an unstable phase is real, and the Universe could decay into an explosion of coalescing bubbles of a new phase. But nothing is conclusive at the moment, due to many uncertainties in the calculation, some controllable (better measurements of particle masses) and some not (new physics at higher energies). Even if the Universe is slated to decay into a new phase, it will take a very very long time.